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Biomedical subjects

R J Bing

Publications and source records attributed to R J Bing.

At least 37 records · Page 2Linked to original sources
PubMed1996

Induction of apoptosis in myocardial infarction and its possible relationship to nitric oxide synthase in macrophages.

Activated macrophages produce nitric oxide through the inducible form of nitric oxide synthase (iNOS). Previously, a significant increase of iNOS activity in macrophages in infarcted rabbit heart tissue was observed. The present study is concerned with the induction of apoptosis in macrophages and cardiomyocytes in infarcted rabbit heart tissue. The left anterior descending artery of rabbits was ligated. The heart was excised five hours, one, two, three, ten and twenty days later, and DNA was extracted from infarcted and non-infarcted region and subjected to electrophoresis. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) was carried out, and iNOS activity was measured by conversion of L-[14C]-arginine to L-[14C]-citrulline. Positive staining by TUNEL was seen in some cardiomyocytes five hours after coronary ligation and on postoperative day (POD) 1; internucleosomal DNA fragmentation was not noted. On POD 2 and 3, many infiltrating cells, immunohistochemically identified as macrophages, were positively stained by TUNEL; DNA fragmentation was also present. Apoptosis was not found on POD 10 and 20. The peak activity of iNOS was noted on POD 3, which corresponded with the induction of apoptosis. It is tempting to speculate that a causal relationship exists between increased iNOS formation and induction of apoptosis in macrophages in infarcted rabbit heart tissue.

Animals↗
PubMed1996

Effect of inhibitors of inducible form of nitric oxide synthase in infarcted heart muscle.

Nitric oxide (NO), an unstable radical, is synthesized from L-arginine by the constitutive (cNOS) and inducible (iNOS) forms of NOS. cNOS is present mainly in endothelial cells and plays a role in the regulation of blood flow. iNOS, the dominant enzyme in heart muscle during myocardial infarction, allograft rejection, and cardiomyopathy, is activated in macrophages. We recently described a significant increase of iNOS activity in macrophages of infarcted rabbit myocardium 24 hours after coronary occlusion, with peak activity occurring 3 days following coronary artery ligation. Inhibitors of NOS are L-arginine derivatives that inhibit both cNOS and iNOS; S-methylisothiourea (SMT) and aminoguanidine (AMG) are specific inhibitors of iNOS. Cyclosporin A and dexamethasone inhibit by interfering with protein synthesis. iNOS inhibition by SMT, NG-nitro-L-arginine (L-NNA), AMG, cyclosporin A and dexamethasone was examined in homogenates of normal, risk and infarcted myocardium. Three days after coronary artery ligation, the heart was excised and divided into normal, risk and infarcted regions. The inhibitory effect was calculated as IC50. Results shows that SMT was the most potent inhibitor with the lowest IC50; its effect, as well as the effects of L-NNA and AMG, depended on the location in the myocardium. Inhibition for SMT and AMG was greater in the normal area than in the risk and infarcted regions. AMG induced an initial rise of iNOS followed by gradual decline in the area of risk and infarction. No inhibitory effects in cyclosporin A and dexamethasone were noted.

Animals↗
PubMed1995

Involvement of inducible nitric oxide synthase in the inflammatory process of myocardial infarction.

Inducible nitric oxide synthase (iNOS), which catalyzes the reaction of L-arginine to L-citrulline and nitric oxide (NO), plays an important role in immune-mediated cardiac disorders. The present report summarizes and discusses findings on the induction of NOS in myocardial infarction of rabbits. iNOS was significantly increased in infarcted myocardium 48 h after coronary artery ligation. The effect persisted for 14 days and declined thereafter. Immunohistochemical localization revealed macrophages as a major source of iNOS expression; iNOS expression was also present in infarcted human myocardium. Increased iNOS activity appeared to be related to the induction of apoptosis in infiltrating macrophages and cardiomyocytes. Moreover, preferential inhibition of iNOS by S-methylisothiourea sulfate (SMT) resulted in significant improvement of left ventricular performance and increased regional myocardial blood flow. These findings suggest that selective inhibition of iNOS activity may provide a therapeutic strategy in cardiac disorders such as myocardial infarction.

Animals↗
PubMed1995

Intracellular translocation of endothelial nitric oxide synthase by lysophosphatidylcholine.

The amphiphile lysophosphatidylcholine (LPC) modulates the activity of membrane-associated enzymes such as phospholipase A2, adenylate and guanylate cyclases and ATPase. LPC also relaxes vascular smooth muscle through production of nitric oxide. On the basis of reports that bradykinin translocates nitric oxide synthase (NOS) from the membrane to the cytosol, we investigated whether a similar translocation occurs with LPC. It was found that LPC translocated NOS from the membrane to the cytosolic fraction. Total NOS activity remained at the control level.

Amino Acid Oxidoreductases↗
PubMed1995

Immunohistochemistry in the identification of nitric oxide synthase isoenzymes in myocardial infarction.

OBJECTIVE: Inducible nitric oxide synthase (iNOS) activity, as measured by conversion of L-14C-arginine to L-14C-citrulline is significantly increased in infarcted rabbit myocardium as compared to healthy myocardium 48 h after coronary occlusion. The aim of this study was to localise the nitric oxide synthase (NOS) isoforms in normal myocardium and compare these findings with NOS activity in cells of the infarcted region. METHODS: Activities of NOS isoforms were enzymatically assayed in normal and infarcted myocardium. Localisation of NOS was performed on identical sections using specific monoclonal IgG antibodies against endothelial constitutive (cNOS) and macrophage inducible (iNOS) nitric oxide synthase. In addition, macrophages were identified using fluorescein conjugated ChromPure rabbit IgG, Fc fragment. RESULTS: iNOS activity increased significantly in infarcted as compared to normal myocardium [0.42(SEM 0.03) v 0.85(0.08) fmol.microgram-1.min-1, P = 0.02, respectively]. However, cNOS did not increase significantly in infarcted regions [0.18(0.04) v 0.24(0.06) fmol.microgram-1.min-1; P = 0.16, respectively]. cNOS was immunohistochemically localised in endothelial and endocardial cells in normal and infarcted tissues. The presence of iNOS activity in macrophages in infarcted myocardium was identified immunohistochemically. Cardiomyocytes and neutrophils did not label with the antibodies to cNOS and iNOS. CONCLUSIONS: (1) Infiltrating macrophages are the main site of increased iNOS activity in infarcted rabbit myocardium. (2) cNOS activity is not significantly increased in infarcted tissues as compared to normal myocardium. (3) Neutrophils and cardiomyocytes do not express NOS immunoreactivity in infarcted and normal rabbit myocardium.

Amino Acid Oxidoreductases↗
PubMed1994

Inducible nitric oxide synthase activity in myocardium after myocardial infarction in rabbit.

The activity of nitric oxide synthase (NOS) in infarcted and noninfarcted rabbit myocardium was determined. NOS activity, as measured by conversion of [14C]arginine to [14C]citrulline, was significantly higher in the infarcted area of myocardium (22.7 +/- 3.7 fmol/mg as compared to 7.67 +/- 1.0 in noninfarcted area). NOS activity within the area of risk remained on control level. Increased inducible NOS activity was observed on the first postoperative day and persisted for at least 14 days; it declined 3 weeks after infarction. Citrulline formation was inhibited by N-omega-nitro-L-arginine and N-omega-monomethyl-L-arginine The localization of NOS by monoclonal anti-NOS antibody indicates mononuclear cells/macrophages as the likely source of the enzyme. The concentrations of tumor necrosis factor-alpha and interleukin-1 beta were not increased in peripheral blood or myocardium.

Amino Acid Oxidoreductases↗
PubMed1994

Dexamethasone inhibits the expression of an inducible nitric oxide synthase in infarcted rabbit myocardium.

Infarcted areas of rabbit myocardium show relatively higher inducible nitric oxide synthase activity, measured by the conversion of L-[14C]arginine to L-[14C]citrulline. The principal finding in this study is that dexamethasone (2 mg/kg) prevents the induction of inducible nitric oxide synthase in heart muscle when given before, or even 3 hr after coronary artery ligation. Additionally cyclic GMP levels remain unchanged following treatment with dexamethasone. It is possible that the enhanced production of nitric oxide by inducible nitric oxide synthase accounts, at least in part, for the depression of myocardial contractility seen in myocardial infarction and in other clinical conditions.

Amino Acid Oxidoreductases↗
PubMed1994

The production of nitric oxide in endothelial cells by amphiphiles.

Lysophosphatidylcholine, an endogenous detergent is an endothelium-dependent smooth muscle relaxant, which acts through the release of nitric oxide. It is known to activate a number of membrane-bound enzymes. Because of the relationship between detergent action, relaxation of endothelium-intact rabbit aortic strips and the release of nitric oxide, we considered the possibility that other amphiphiles also produce nitric oxide from endothelial cells. We therefore investigated the effect of digitonin on relaxation of precontracted rabbit aortic strips and the release of nitric oxide from freshly harvested bovine endothelial cells as determined by chemiluminescence. We found that both digitonin and LPC release nitric oxide and that this process is inhibited by the NO synthase inhibitor N omega-Nitro-L-Arginine Methyl Ester (L-NNAME).

Animals↗
PubMed1994

Effect of amphiphiles on nitric oxide synthase in endothelial cells.

Amphiphiles are known to modulate the activity of ATPase, phospholipase A2, adenylate and guanylate cyclase amongst others and relax vascular smooth muscle. The effect of two amphiphiles, lysophosphatidylcholine (LPC) and digitonin on the activity of nitric oxide synthase (NOS), as measured by conversion of radiolabeled L-arginine to L-citrulline, has been studied. Neither digitonin (0.01 mmol/l) nor LPC (0.01 mmol/l) influenced NOS activity in endothelial cell homogenates. Digitonin but not LPC stimulated NOS in intact endothelial cells. NOS activity was markedly inhibited by L- but not by D-omega-nitroarginine (D-NNA, 0.1 mmol/l). L-NNA or D-NNA data demonstrate no effect of amphiphiles on isolated NOS. NOS activation may occur as a result of detergent action on the membrane.

Amino Acid Oxidoreductases↗
PubMed1993

Synthesis of leukotrienes by freshly harvested endothelial cells.

Endothelial cells produce endothelin, a powerful vasoconstrictor. We report the release of additional vasoconstrictor material in conditional filtrate from freshly harvested cells, which we identified as leukotrienes by radioimmunoassay (RIA) and by high pressure liquid chromatography (HPLC). The material was collected in cell free filtrates by superfusion of freshly harvested bovine endothelial cells attached to cytodex-3 microcarrier beads. Cells and beads form a dense network on filter paper permitting collection of cell free filtrate. The amount of leukotrienes in conditioned filtrate was 158 +/- 21 picograms/million cells. The calcium ionophore A23187 stimulated the release of leukotrienes (392.0 +/- 47.6). The peak of leukotriene production occurred within an hour after incubation of cells slowly declining thereafter. Conditioned filtrate to which indomethacin had been added caused coronary vasoconstriction in the perfused rat heart preparation, as did synthetic leukotrienes C4, D4 and E4. It was found by RIA and HPLC that some of the constrictor effect of conditioned filtrate derived from leukotrienes.

Animals↗
PubMed1993

Membrane function and vascular reactivity.

This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates sialyltransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.

Animals↗
PubMed1993

Vascular smooth muscle and nitric oxide.

Experiments were performed to investigate the production of endothelium-derived relaxing factor (EDRF or nitric oxide; NO) by vascular smooth muscle cells. The lumen of bovine pulmonary arteries were filled with Krebs-Henseleit solution (incubates). Both endothelium-intact and endothelium-deprived vessels were used. Incubate solutions from the lumen of generator vessels contained a significant amount of nitric oxide (NO). Although the NO concentration was higher in incubates from endothelium-intact vessels, endothelium-deprived vessels also produced NO. The length of incubation did not influence the amount of nitric oxide released. Endothelium-deprived pulmonary arteries also generated NO as detected by chemiluminescence. The amount produced however was not sufficient to relax endothelium-deprived detector vessels in superfusion bioassay experiments. Samples from Krebs-Henseleit (K-H) solution surrounding the preparation (bathing solution) contained NO values which were also significantly higher than the control. Nitric oxide found in the bathing solution also appeared to originate from endothelium and vascular smooth muscle. Oxyhemoglobin attenuated NO signals. The results demonstrate that nitric oxide is released by vascular smooth muscle cells as well as by endothelium. However, the amount of NO released by muscle is insufficient to relax endothelium-deprived vascular preparations.

Animals↗
PubMed1993

The production of coronary vasoconstrictor substances by freshly harvested endothelial cells.

The effects of cell free superfusates from freshly harvested bovine endothelial cells attached to microcarrier beads on the isolated rabbit and rat heart and on superfused rabbit jugular veins were observed. Cell free conditioned filtrates from freshly harvested cells caused marked diminution in coronary flow and cardiac output in the isolated rabbit heart; in the perfused rat heart an increase in coronary perfusion pressure and a decline in left ventricular systolic tension and maximal left ventricular contractility (dP/dt) were recorded. Marked differences were found between changes induced by conditioned filtrate as compared to synthetic endothelin. Endothelin as present in conditioned filtrate could not account for the pronounced effect on coronary perfusion pressure, dp/dt and cardiac output induced by conditioned filtrate; more than one hundred times that of synthetic endothelin was needed to achieve comparable cardiodynamic effects. This suggested that additional non-prostanoid vasoconstrictor substance or substances are produced by freshly harvested endothelial cells. This conclusion was supported by the observation that BQ-123, a specific inhibitor of endothelin A (ETA) receptor significantly prevented contractions by endothelin, while failing to inhibit those induced by freshly harvested endothelial cells. These constrictor substances may be leukotrienes.

Animals↗